The undersea explorer who decades ago discovered North America's first authenticated pirate shipwreck believes he's found where its legendary treasure lies off Cape Cod.

Barry Clifford tells The Associated Press his expedition recently located a large metallic mass that he's convinced represents most, if not all, of the 400,000 coins and other riches allegedly contained on the ship named the Whydah Gally (WIH'-duh GAH'-lee).

The 71-year-old explorer hopes to start investigating the suspected riches this month.

But Smithsonian curator Paul Johnston says Clifford needs to provide more concrete proof before he can satisfy skeptics. Clifford has been wrong before after touting finds at other shipwrecks.

The Whydah Gally went down in stormy seas in 1717 and nearly all of its roughly 150-person crew perished, including the pirate captain Samuel "Black Sam" Bellamy. It was discovered in 1984.